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While researching motor oil requirements for old engines, I came across some manuals that show how little has changed over the years. Please notice how similar the1938 Dodge owner's manual is to the 1965 Valiant owner's manual.

1938 Dodge D-8 Owners Manual Recommendations

Draining the Crankcase and Crankcase Ventilation (Prolongs Engine Life)

Due to natural conditions in all automotive engines, the engine oil, in use, is constantly being impregnated with fuel, water, and acid, depreciating the the value of the oil as a lubricant. However, a ventilation system has been built into the engine in your car which expels a very large percentage of of these undesirable elements. With this ventilation, the frequency of draining the crankcase oil is also reduced, but nevertheless it is necessary to drain at the intervals specified.

Fuel accumulates in the engine oil because of certain excess of fuel in the combustion chambers not burning and working down the cylinder walls into the crankcase. Only certain percentages of vaporized fuel and air, when mixed, will ignited and explode in the combustion chamber. If the mixture contains too much fuel, the excess will not burn, some of it will remain on the cylinder walls and work down into the crankcase by the action of the pistons.

Water vapor is a product of combustion. There is approximately as much water vapor formed by weight as fuel consumed. Thais why you may notice white vapors and water coming out of the exhaust pipe, especially in cold weather. A certain amount of the vapor condenses on the cylinder walls and is also carried into the the crankcase by action of the pistons. A very large percentage of this water and fuel is carried out of the crankcase by means of the crankcase ventilation system.

Fresh air enters at the oil filler pipe which is capped with an air cleaner for catching dust and preventing it entering the crankcase. Due to the rotation of the crankshaft, the air and vapor in the crankcase is kept whirling. The vacuum created by the car running draws the air and vapor out of the crankcase through the ventilation outlet pipe at the rear of the engine.

This system of crankcase ventilation, as you can no doubt readily understand, reduces to a great extent a natural formation of sludge in the bottom of the crankcase. An excess amount of this sludge will interfere with proper engine lubrication.

Acid forms in the combustion chamber also due to natural causes in all automotive engines. Fuel contains varying percentages of sulphur and, when burned, changes to sulphur dioxide. The sulphur dioxide unites with water in the combustion chamber, making sulphurous acid.

These accumulated non-lubricating elements in the engine oil have damaging effects on the highly finished steel surfaces. Fuel thins the oil, reducing its lubricating ability. Water is a non-lubricant and is likely to freeze, causing stoppage of the oil circulation. The sulphurous acid attacks the highly finished steel surfaces and causes excessive wear. The rapidity of of accumulation of these elements increases as the temperature decreases. That is why it is recommended that the engine oil be drained more frequently in cold weather than in warm weather.

The best time to drain the crankcase is after a run and while the engine is still heated. The oil is thinner when it is hot and also thoroughly mixed. It will therefore carry off sediment more completely.

Kerosene should never be used for flushing out the oil pan and lubricating system. A certain amount will remain in the system, collecting in pockets from which it cannot readily be drained and will dilute the oil. For flushing, always use a good flushing oil.

Engine Oil Recommendations

Custom, in the past, was to use heavier (thicker) oils than at present. The use of light engine oil is an aid in cold weather starting, fuel economy, and the proper lubrication of parts.

To assist the selection of oil having the proper viscosity, select a recommended oil for the next lower minimum temperature point than the anticipated lowest temperature. During the winter, if there is any doubt as to the viscosity of oil to use, always select the grade with one lower viscosity number to insure ease of starting. During winter, all oils used should have a pour point or cold test below the lowest anticipated temperature that will be encountered during its use.

After the engine is broken in, oil changes should be made every 1500-2000 miles in winter and every 2500-3000 miles in summer.

SAE Viscosity Temperature Range
SAE 40
  • average daytime temperature of 90°F, which means:
    • continuously recurring morning temperature of 70-80°F
    • mid-afternoon peak temperature of 100-110°F
SAE 30
  • above 32°F
SAE 20-W
  • above +10°F
SAE 10-W
  • above -10°F
SAE 10-W (plus 10% kerosene)
  • above -25°F

When to Change the Engine Oil

In new cars, the oil should be drained out at about the first 500 miles of operation and refilled with an oil not heavier than No. 10-W during the winter, or heavier than SAE 20 or No. 20-W during the summer. The next oil change should be at 1500 miles speedometer reading and refilled with the viscosity of oil as recommended by the chart. After these initial changes of oil, if the driving conditions are normal, oil changes should be made every 1500 to 2000 miles in the winter and every 2500 to 3000 miles in summer.

It is always advisable to drain the crankcase while the engine is at normal operating temperature. Oil will drain more completely when hot, and will, therefore, carry more of the foreign material and dirt with it if drained while the engine is warm.

Dust Roads and Dust Storms

Driving over dusty roads or through dust storms introduces abrasive material into the engine. Air cleaners which are kept in good clean condition decrease the amount of dust that may enter the crankcase. However, if the oil become contaminated with dust or dirt, it should be drained promptly to prevent harmful engine wear. The frequency of draining depends upon the severity of the dust conditions and no definite draining periods can be recommended. It should be remembered that an oil change to eliminate abrasive dust may be considerably cheaper than to take a chance on worn engine parts.

Winter Driving

During winter, if the car is driven for short distances of only a few miles at a time, water will condense in the crankcase and form a sludge which may freeze and clog the oil inlet screen. This is especially true if winter temperatures are extremely low for an extended period of time. Under conditions of this kind, the engine does not become sufficiently warm to expel the water through the crankcase ventilation system, and the oil should , therefore, be changed about every 500 miles, and under extreme conditions, less than 500 miles, to eliminate sludge. The engine should be thoroughly warm before it is drained.

As an alternative to this frequent change period during winter, an occasional drive of 30 miles or more at speeds of 50 miles per hour or higher, will do much to eliminate the water through the crankcase ventilation system and the change period may be extended to 1000 miles, or the normally recommended 1500 miles winter change if these longer drives are indulged in frequently.

The Oil Filter

The function of the oil filter is to remove dirt and foreign material from the oil in order to assist in keeping the oil clean. This is a continuous process, and the filter cartridge will continue to trap dirt until it becomes clogged. Due to the manner of connecting the oil filter to the oiling system, clogging of the filter will not stop the circulation of oil to the bearings. However, when the oil filter is clogged, it ceases to filter the oil. It is, therefore, advisable to install a new oil filter every 8000 miles. In dusty areas, it may be advisable to examine the oil and change filters more frequently, or at any time when the oil appears to be excessively dirty.